Various sensors are known in the pressure sensing arts. Pressure transducers are well known in the art. One example of a pressure transducer is a device formed with a silicon substrate and an epitaxial layer, which is grown on the substrate. A portion of the substrate can then be removed, leaving a thin, flexible diaphragm portion. Sensing components can be located in the diaphragm portion to form a pressure transducer. In operation, at least one surface of the diaphragm can be exposed to a process pressure. The diaphragm deflects according to the magnitude of the pressure, and this deflection bends the attached sensing components. Bending of the diaphragm creates a change in the resistance value of the sensing components, which can be reflected as a change in the output voltage signal of a resistive bridge formed at least partially by the sensing components.
Some techniques for forming a composite diaphragm for a pressure transducer or similar device involve configuring a substrate layer having a first conductivity type, wherein the substrate layer includes a first surface. Positive implants can then be deposited in the first surface of the substrate layer, and an epitaxial layer grown on the first surface of the substrate layer so that the positive implants form positive diffusions in the epitaxial layer. An oxide pattern can be then formed on the epitaxial layer, and a top layer deposited over the epitaxial layer and oxide pattern. The substrate layer and positive diffusions of the epitaxial layer can then be etched to form the composite diaphragm. Such a composite diaphragm can therefore be provided for use in a pressure sensor or like device. The diaphragm comprises a first layer of silicon nitride and a second layer attached to the silicon nitride layer and comprising a pressure sensor pattern of silicon material.
Pressure transducers of the type which comprise a thin, relatively flexible diaphragm portion of suitable material, such as silicon or ceramic, on which either a selected resistive element or a capacitive plate is printed whereby exposure to a pressure source causes deflection of the diaphragm will cause a change in the resistive value of the resistive element or a change in the spacing of the capacitive plate with a mating capacitive plate and concomitantly a change in capacitance are therefore well known in the art.
One area where pressure sensors find critical usage is in the natural gas production and distribution industry. The ability to monitor natural gas line pressures over a wide temperature and pressure range is important in many residential, consumers, commercial and industrial settings. Safety remains a constant concern in any situation in which natural gas is distributed.
For some industrial applications such as, for example, the distribution of combustible process fluids (e.g., combustible gases), explosion proof or flame proof rated regulators, sensing devices, etc. are required. In the case of a regulator, combustible process fluids that accumulate in the regulator housing must be properly vented to ambient or atmosphere to achieve a flame proof or explosion proof rating. Generally, atmospheric venting is configured to prevent the dangerous accumulation of combustible process fluids within the regulator housing and to prevent a combustion process that initiates within the regulator housing from propagating to the greater process ambient surrounding the regulator. For example, one or more sintered metal flame arrestors (which are semi-porous and provide a sufficiently minimal flame path) may be used to provide the necessary atmospheric venting.
Based on the foregoing, it can be appreciated that there exists a continuing need for improved pressure sensors, which can be adapted for use in monitoring hazardous fluids and gases, such as that present in a natural gas line. Not only is safety a factor, but cost is also a concern. A need exists for a highly accurate and low cost pressure sensor for such situations.